Afterburner nozzle



- May 2, 1961 w. F. EGBERT AFTERBURNER NOZZLE Filed June 24, 1955 3 Sheets-Sheet 1 ATTORNEY May 2, 1961 w. F. EGBERT AFTERBURNER NOZZLE 3 Sheets-Sheet 2 Filed June 24, 1955 INVENTOR. 4 /122 .2

ATTORNEY May 2, 1961 w. F. EGBERT AFTERBURNER NOZZLE 3 Sheets-Sheet 3 Filed June 24, 1955 INVENTOR. Z /2%'4/7 ffifiaif BY ATTORNEY 2,982,089 AFTERBURNER NOZZLE William-F. Egbert, Brownsburg, 1nd,, assignor to Genera] Motors Corporation, Detroit, Mich., a; corporation ofiDelaware.

Filed June 24, 1955,.Ser. No. 517,779 6 Claims (Cl-a 60:. 35i6) 1 This invention relates to. turbojet aircraft: engines, and more particularly to exhaust nozzle arrangcmcntstherefor. 7 i

The invention is primarily: concernedwithi high pressure ratio, afterburner-equipped, turbojet engines, that are capable of propelling aircraft at; supersonic peeds. The turbine exhaust gas. of such an" engine is at a. relatively high temperature, high pressure and. lowqvelocity and is expanded to atmosphere through a suitable nozzle at a relatively high, velocity, low temperature and. low pressure to power the aircraft. The exhaust jet velocity at the nozzle outlet is a function of the turbine outlet vtemperatureand of theexpansion ratio through the nozzle. .Maximum use of, the available energy in the turbine exhaust gas of a high pressure ratio turbojet engine can. be ob tained by complete expansion of the exhaust gas; to ambient pressure through a convergent-divergent nozzle. For best ,efficiency under various operating nditimls it is desirable that the convergent-divergent nozzle beprovided with means to vary its discharge Or outlet area and with means to vary its throat area.

An object of the invention is to provide a nozzle arrangement that will have a wide range of area variation and that will meet the rigid strength and weight requirements of aircraft engine practice.

In physical form the invention embodies a plurality of cooperating means for varying the area of the nozzle and includes a plurality of overlapping arcuate nozzle flaps that are pivoted about the reduced end of an afterburner exhaust duct. The nozzle flaps are provided with generally radial cam slots and the hoop end of an actuating cage rides in the cam slots to impart opening and closing movement to the nozzle flaps on axial movement of the cage. A tailcone is located within the exhaust duct with patented May 2,1861

I Figure 4 is a. partial section that corresponds to Figure 3, illustrating the nozzle in closed position; anda Figure 5 is a partial section that corresponds: to Figure 4 but illustrating the exhaust duct retracted forwardly to encircle the tailcone and thus introduce, the end portion of the tailcone into the throat of the nozzle.

Referring 'now to Figure l, a substantially. annular: turbojetengine 10 of known design is supported in. the annular interior of an aircraft nacelle 12'. The turbojet engine includes a compressor 14- which receives air from the nacelle inlet 16 and delivers it to the combustor18 its rearward end proximate the nozzle flaps and the after- 7 burner exhaust duct is axially shiftable with respect to the tailcone to shift the nozzle flaps into and out of encircling relation with the tailcone. The throat and outlet areas of the nozzle are varied concurrently by radially opening and closing the nozzle flap's. Additional nozzle area variation is achieved by axially shifting the nozzle flaps into or out of encircling relation with the tailcone. The latter area variation can take place independently of the former so that the throat area can be varied without concurrent outlet area variation.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a side view of an aircraft turbojet installation, partially broken away;

Figure 2 is a partial longitudinal section of the exhaust portion of the engine substantially enlarged to illustrate a nozzle flap at its point'of attachment;

Figure 3 is a partial longitudinal section of the exhaust portion of the engine illustrating the nozzle inopen position and with the exhaust duct extended rearwardly to clear the nozzle throat of the tailcone;

for expansion through a turbine 20 that drives the compressor. The exhaust gas from the turbine passes through an: annular diffuser casing 22 and' an afterburner 24.

Referringito the remaining figures, an exhaust duct 26 ing ribs 28. Split expansion rings 30 and 32 prevent. the

high pressure exhaust gas from escaping between: the afterburner casing 24 and the exhaust pipe 26., A longitudinallymovable actuating rod 34 is secured to the ex.- haust duct 26 to impart axial movement thereto.

The high velocity exhaust gas is emitted from theex haust pipe 26. through avariable area jet nozzle 3.6- to drive the'aircraft. The nozzle is fashioned from a: plurality of overlapping flaps or staves- 38 of generally T section, each pivotally secured to the reduced end 40 of. the exhaust duct 26. by arcuate tongues 42 that lie. in acomespending annular groove inthe exhaust duct extremity. Each nozzle. flap 38 has a radially extending; side plate46 secured thereto to: form a camslot 48 that extends at: an acute angle to the longitudinal or center line ofv the. engine. An actuator 50. includes acylinder- 52 supported for axial mov ment; on he exhau t, pipe :26va-nd. under the control of an actuating rod 54. The actuator 50 carries a projecting cage-like structure that includes a plurality of longitudinal bars 56 and a hoop that rides in the cam slots 48 to swing the nozzle flaps 38 inwardly and outwardly in a radial sense on axial shifting of the hoop to vary the flow condition in the nozzle. A fixed tailcone 58 is located in the exhaust pipe 26 with its conical end 60 proximate the nozzle flaps 38. The nozzle flaps- 38 have substantially parabolic curvature and are pivoted at their more highly curved end to the reduced end 40 of the exhaust pipe to provide a variable area convergent-divergent nozzle.

By reference to Figures 3 and 4, 'it can be seen that the exhaust outlet radius E and the exhaust throat radius E,

are garied concurrently by axial movement of the actuator 0.

In installations where the engine temporarily operates at a low pressure ratio, the exhaust nozzle should have a converging range as well as a converging-diverging range. This is readily accomplished by increasing the slope of the cam slots 48 of the exhaust nozzle flaps 38, as shown by the dotted lines of Figure 4, so that the exhaust throat outlet E, continues to move rearwardly towards the exhaust outlet E on rearward movement of the actuator 50 until the throat and outlet coincide to achieve a purely convergent nozzle.

By reference to Figure 5, it can be seen that the effective exhaust throat radius E, can be varied without afiecting the exhaust outlet radius E by axially shifting the exhaust pipe 26 and the associated nozzle flaps 38 with respect to the fixed tailcone 58 so as to introduce the pointed end of the tailcone into the center portion of the nozzle. The effective exhaust outlet radius E can also be varied if sufiicient axial shifting takes place to introduce the tailcone into the nozzle outlet. The nozzle flap actuating rod 54 and the exhaust pipe actuating rod 34 are preferably operated independently of each other but it should he realized that they could be operated concurrently in a coordinated manner, if desired.

Major design improvements to present day aircraft turbojet engines have resulted in greatly increased thrust ratings with but little diameter increases thereby maintaining the frontal area of the engines at a minimum and avoiding parasitic drag increases. The variable 'area exhaust nozzle of the invention is particularly adapted for high thrust, small diameter engines as the cooperating dual means for varying the exhaust nozzle area allows an eflicient wide range of operability without increasing the diameter of the engines. The invention accomplishes this because a sizable percentage of area variation is obtained by the axial movement of the nozzle flaps with respect to the 'tailcone. i 1 ';-While the preferred embodiment of the invention has been described fullyin order to explain theprinciples of the invention, it is to be understood that modifications of structure may be made bythe exercise of skill in the art within the scope of the invention which is 'not to be regarded as limited by the detailed description of the preferred embodiment. I claim: i

1. A turbojet engine comprising an exhaust duct having a reduced end, a tailcone in the exhaust duct having a tapered end proximate the reduced end of the exhaust duct, and an exhaust nozzle comprising a plurality of I operation as well as a variable area convergent-divergent range of operation.

3. Apparatus in accordance with claim 1 including an axially shiftable hoop about said flaps and a cam connection between said hoop and flaps to swing said flaps radially on axial shifting of said hoop, a first actuator for axially shifting said hoop, and a second actuator for axially shitting said exhaust duct and said flaps.

4. Apparatus in accordance with claim 1 wherein said exhaust duct and flaps are axially shiftable independently of pivotal movement of said flaps whereby area variation of the nozzle throat can take place without area variation of the nozzle outlet.

5. Apparatus as claimed in claim 1 wherein the flaps are substantially parabolic, wherein the nozzle outlet is formed by the flat portion of the parabola, wherein the nozzle throat is formed by the curved portion of the parabola, and wherein the end of the tailcone is of conical configuration.

6. Apparatus in accordance with claim 5 including an axially shiftable hoop about said flaps and a cam connection between said hoop and flaps to swing said flaps radi-' ally on axial shifting of said hoop, said hoop being axially shiftable independently ofrelative axial movement beflaps, curved to provide inner surfaces convex in longitudinal cross section and pivotally secured to the reduced exhaust nozzle has a variable area convergent range'of tween said exhaust duct and said'tailcone.

References Cited in the file of, this patent UNITED STATES PATENTS 750,307 Great Britain (duplicate) June 13,1956 

